AN-92-16-1 RESIDENTIAL KITCHEN VENTILATION - A GUIDE FOR THE SPECIFYING ENGINEER
D.W. Wolbrink J.R. Sarnosky, P.E. Member ASHRAE
ABSTRACT The hood provided an inverted sump to capture the convective flow and the fan extracted the captured air. It r The evolution of residential kitchen ventilation is actually worked well and revolutionized residential kitchen examined a/Id the importance of kitchen range hoods in ventilation. today's ventilation systems is reviewed as an aid to the Today's powered residential range hood came into specifying engineer. Home cooking produces liquid a/Id being when engineers unitized the hood, putting the fan solid particles, odors, airborne moisture, heat, and inside the hood at the factory, so their company could sell sometimes gas combustion products. How the residential one product where before they had sold two. With the range hood handles these problems is revealed, and the addition of an effective light for the cooking surface, the results of various testing programs are given. The proper present standard configuration of the product appeared. application of range hoods relative to sizing, room Ductless hoods, althoughnotventilatingdevices, must location, a/Id proper ductwork is discussed. 1he rating be mentioned as part of kitchen ventilation history. They methods a/Id standards for hoods are explained and appeared on the scene just after the Nautilus submarine related to real life. The issues of range hood noise and traveled under tlie polar ice cap in the 1950s. There was energy conservation are reviewed a/Id answers are great public awareness of the use of activated carbon provided on how to ha/Idle these issues. Current standards (charcoal) as an adsorbent for maintaining the quality of a/Id codes dealing with kitchen ventilation are reviewed. the air on board the submarine. The time was ripe for the The future of kitchen ventilation in home construction is introduction of the "charcoal" range hood. Today those predicted and discusse~ / hoods are sold in considerable volume, even though their contribution to improved residential air quality is not INTRODUCTION exciting. In fact, manufacturers of ductless hoods make no claims for their performance as ventilating equipment. Cooking generates pollution, so the history of kitchen ventilation goes back to early times. History can provide Kitchen Ventilation Is Important insights into the mechanics of the ventilation process. By to Residential Air Quality quantifying the parameters associated with cooking and ventilation, problems will be solved easily and effectively. It is important now for ASHRAE engineers to appreciate the importance of kitchen ventilation in the History of Kitchen Ventilation total scheme of residential indoor air quality. Residential air quality is becoming increasingly important to the Kitchen ventilation has always been important to public. They are demanding better ventilation in their comfort and health, but people have only recently become homes, and specifying engineers need to be proficient in m~ch more aware of it. Even in the stereotyped tepee of designing systems that will meet their expectations. the early Native Americans, there was a flap in the top to How will ASHRAE meet this challenge? It is already let the smoke out. Early American settlers used fireplaces doing so. It started with a new interest in residential for cooking, where the convective currents flowed up the energy conservation. ASHRAE responded appropriately chimney and makeup air ..came in through the cracks in by splitting ASHRAE Standard 90, Energy Conservation the structure. in New Building Design, into 90.1 (larger buildings) and Many of us remember when open windows provided 90.2 (residential). That was a landmark of sorts, a the needed ventilation .. They were replaced by through significant venture by ASHRAE into the residential field. the-wall fans, often equipped with a pull chain; even those As with energy, it is now appropriate to emphasire the have been around for a couple of generations. residential aspects of ventilation. ASHRAE Standard 62, In the 1950s the first version of an effective working Ventilation for Acceptable Indoor Air Quality, covers kitchen range hood appeared. It was a separate metal both commercial and, to some degree, residential ap hood, mounted over the cooking range. The traditional plications, but residential information is scanty and is fan was installed through the wan just below the hood. wri~ten as an offshoot of commercial. It is important that David W. Wolbrink is vice-president of engineering and Joseph R. Sarnosky is a project engineer at Broan Manufacturing Co., Inc., Hartford, WI. THIS PREPRINT IS FOR DISCUSSION PURPOSES ONLY, FOR INCLUSION IN ASHRAE TRANSACTIONS 1992, V. 98, Pt. 1. Not to be reprinted in whole or in part without written permission of the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Inc., 179) Tullio Circle •. NE, Atlanta, GA 30329. Opinions, findings, conclusions, or recommendations expreBBed in this paper are those of the 11uthor(sl 11nd do not necessarily reflectthe views of ASHRAE. Written questions and comments regarding this paper should be received at ASHRAE no later than Feb. 7, 1992. residential ventilation should gain its own coverage indoor air quality, and today's ho118e8 don't leak enough because the residential concerns are unique. to cover up problems. Specifying engineers must and will With improved energy performance of residential become involved. building construction, it has become apparent that residen This paper will explain how to be successful when tial ventilation has two distinct parts: specifying intermittent kitchen ventilation and why, especially for the engineer, the necessary recommen 1. continuous ventilation, directoo toward those pol dations are made. lutants that are produced continuously, including such sources as respiration, perspiration, and emissions from building materials, and FACTORS RELATED TO KITCHEN VENTILATION 2. intermittent ventilation, directed toward those pol lutants that are produced intermittently, including To deal effectively with kitchen ventilntion, 11 knowl those produced by showering, cooking, bathroom edge of cooking contaminants is essential. Then the use, and smoking. performance of hoods against those contaminants can be evaluated and a method of quantitatively measuring that Why are there two parts? First, the intermittent performance can be developed. pollutants must be controlled as part of source mitigation, the first step toward indoor air quality. If not mitigated, Contaminants in the Kitchen the contaminants can be harmful, either causing damage or introducing harmful pollutants through recirculation, so What is the character of kitchen contamination? First, intermittent ventilation is required in the kitchen if the contamination is produced at a high level of con continuous ventilation is to work satisfactorily. centration over a short time. Second, there are a variety Second, continuous ventilation must be at a relatively of contaminants involved, including particulate matter, low rate because of energy costs, but that low rate is moisture, heat, odors, and gases, and this variety of inadequate to control intermittent pollutants because of the contaminants can be produced in a variety of combina high generation rates. Cain et al. (1979) found that some tions. contaminants (tobacco smoke) are not controlled by Particles can be formed in several ways. Both solid ventilation rates of a fraction of an air change per hour. and liquid particles are generated in cooking. The solid It is not practical to control high concentrations of particles are usually a result of an error in cooking that intermittent pollutants with continuous ventilation because causes the food to bum, generating carbonaceous par economics and comfort do not permit the necessary high ticles. Vegetables in particular are of a cellulosic nature, rate of ventilation. and they readily form these solid particles when burned. History helps emphasize the distinction between the These "burning" incidents are infrequent but still must be character of continuous and intermittent ventilation. The kept in mind because particles are produced. continuous ventilation of pre-oil-embargo houses was The liquid particles formed are the most important. provided by natural infiltration, usually found to be They are produced in two distinct size ranges. The large between 0.5 and 2.0 air changes per hour (ach). Intermit liquid particles form through minor explosions within the tent ventilation in those same houses was usually provided cooking vessel, and they are visible as they move through by an openable window in the kitchen and bath (with the air and spatter on the surrounding surfaces. The mechanical ventilation as an acceptable alternative in most explosions occur when water contained within the food is codes and standards). introduced into hot liquid grease or oil. The high tempera Today continuous ventilation is sometimes provided ture of the oil causes the water contained in the food to by "whole house" systems with a ventilation rate of 0.3 flash over explosively into steam, spattering the liquid to 0.5 air changes per hour. Intermittent ventilation in grease. The size of the particles formed this way ensures these houses is provided through .\citchen range hoods and that most will quickly fall back onto the adjacent surfaces bathroom exhaust fans. If the high concentrations of due to gravitational forces, but some can become airborne intermittent pollutants are not mitigated, the continuous and drift about before falling. These particles are too ventilating system cannot provide the expected air quality large to be removed by residential ventilation equipment, within a reasonable period of time. but fortunately they do not go far past the immediate So ventilating range hoods are important, and it is cooking area. timely to report on some of the functional measuring and In contrast, the more common liquid particles are testing that has been done to quantify range hood ven very small. They remain airborne and drift about before tilation performance. Often in the past, specifying en settling on walls, drapes, and other surfaces throughout gineers were not involved in the specification of residen the home. These particles are generated by a different tial hoods, which was acceptable because the infiltration process. wlien the oils from cooking are heated to rate was high and the occupants were not as knowledge elevated temperatures, there is evaporation. A mixture of able as they are today. Now people know more about warm air and warm evaporated oil molecules is carried upward away from the cooktop by the thermal currents of very small particles can be seen as a cloud. The bluish generated by the hot surfaces of the cooktop. As the color indicates the suspended particles are 0.3 to 0.4 µm mixture travels the short distance into a cooler region of in diameter. At that size they are the same size as the the room, the evaporation is reversed. The oil vapor wavelength of visible blue light and the light-scattering condenses into a liquid and is converted into very small effects are particularly intense (Sarnosky 1987). This was particles. The particle formation process depends on both remarkably obvious in some of the work done on particle the thermodynamics of the system and on the available generation. nucleation potential of the system. There follows a small · In the study of kitchen contaminants and particulate amount of agglomeration, but most of the condensed matter, we measured particle size using a quartz crystal particles remain very small. cascade microbalance particle impactor. This is a 10- There is a difference of several orders of magnitude stage, cascade-type particle separator that uses two tuned in the mass and volume of the particles produced by the collecting crystals in a 10-kHz oscillator in each stage to condensation mechanism and the explosive spatter mode. measure the mass collected. It provided multiple con Studies of the spatter particles show them to be in the 10 secutive samples of particle concentration in a short time to 100 micrometer (µm} range, and 50% are less than 80 and was a self-contained portable instrument that was µm in diameter (Annis and Annis 1964). These heavy easily moved from the laboratory to a residential kitchen spatter particles fall to nearby surfaces due to gravity. for study in both situations. Small condensation particles have been measured by the Our first particle studies were conducted in a simu authors and have been found to be in the range of 0.01 to lated scaled-down kitchen. A nonabsorbent sealed room 3.0 µm. These particles float in the air and are moved was constructed as shown in Figure 1. around by Brownian motion and convective currents. In studying particles, fresh com oil was heated to They are typical aerosols with very slow settling rates, cooking temperatures (400°F} for 30 to 60 minutes and while particles larger than 5 µm settle rapidly. particle concentration in the room was measured. When Typical settling rates for particles of various size are the concentration level stabilized, the heat was discon given below: tinued and concentrations monitored over a period of 4 to Time to Fall 72 hours. From these tests we determined particle size, Particle Size One Foot in Still Air particle production rate, saturation time, and decay rate of (micrometers) (minutes) particle concentration. Figure 2 shows the persistence of } very small particles in the room over several hours. 0.3 1, 100.0 We then studied particle generation in a 40-year-old 1.0 122.0 house. The cascade impactor was set up in the kitchen 5.0 6.0 and particle generation measured as a result of cooking 10.0 1.6 typical foods such as bacon, pancakes, eggs, french fries, 20.0 0.43 and hamburgers. Figure 3 shows the particle concentration 100.0 0.021 levels in the kitchen. Our conclusions from these studies show there is a preponderance of particles less than 1.2 This information is based on Stokes' law and assumes µm in diameter that are generated and continue to persist particles in still air that are not being influenced by other in the kitchen. Unless these particles are removed, they forces such as thermal currents and electrostatic charges. will eventually settle on the available surfaces and lead to The condensed particles tend to remain airborne almost soiling, residual odors, and other problems. indefinitely, even if they leave the house by exfiltration, The cooking process also can generate excessively until they agglomerate into larger particles and fall or are large quantities of water vapor. The ubiquitous nature of attracted to the surrounding surfaces by electrostatic or this water vapor causes it to mix readily into the im thermal forces. mediate area and to diffuse rapidly, establishing a high Typical particle sizes for some materials are humidity level throughout the dwelling. Excessively high ,• moisture content in the home can be a problem, as was -Tobacco smoke averages 0.3 µmin diameter. dramatically shown by the difficulties experienced with -Dust ranges from 0.01 to 20 µmin diameter. some prefabricated home units in Wisconsin and Min -Pollen ranges from 10 to 100 µmin diameter. nesota. -The point of a straight pin is 15 µm in diameter. That situation came to public attention after a phy -Human hair is 100 µmin diameter. sician correlated an abnormally high incidence of respira tory problems and general malaise with a specific part of Volatilized kitchen oil particles are in the same size range the community where all the houses were prefab units as tobacco smoke and some dust, and they settle at the built by the same firm (which is no longer in business). same rate. The houses were of modest size and were unusually Particles are not visible individually unless they are airtight. Further investigation showed a high population greater than about 10 µmin diameter. Massive numbers per square foot of living space and inadequate ventilation CAB CAB CAB CHAMBER SIZE 8'-0" l 8'-0" l 8'-0" - -
PURGE I FLOW OUTLET SPLITTER CAB I CABINET LAYOUT / SAMPLE TUBE
PURGE INLET I COOK TOP CENTERED DISTRIBUTORS 12) BENCH ON CABINET W/Q.C.M.B. CASCADE I PARTICLE BLWR IMPACTOR
Figure 1
TEST KITCHEN 11/6/85
"a: 100 ~ 2 1200 /' a: w "' I 90 Q. I I TEST DUCT ~ 1000 I If) \ i-- a: \ z (!)"' \ 0 0 a: 80 v:::: ['j 800 I ~ ~ I >V rl\L u I/ :§ :ii ( v l - FRE~ ~ v- I FRIES I "! 600 ' / I 70 - I z 1 z I ...... 60 MICRON 0 aDAMPER ORIFICE PLATE '-... CAl!llNl!T 2 REQ'D 15 x 12 x 30 30" RANGE HOOD CABINET 48 x 24 x 30 ...... CLEAN ROOM 8' x 8' x 8' Figure 6 it out of the kitchen. It functions like an inverted base room, and the mean value of water concentration in the ment sump pump. The sump holds the water and the room is thus determined. Wet- and dry-bulb temperatures pump moves it out. It is therefore important to design the of air entering and leaving the room are measured and hpod so it has enough inverted volume to hold the wa_ter vapor content is likewise determined. This infor cooking effluent. It must be easy for the effluent to enter mation is combined in the rate flow equilibrium cal the hood, which calls for an open perimeter. The front-to culations to give a final hood capture efficiency. back dimension of the hood is important; it must extend The derivation of hood capture efficiency is based on far enough forward to cover the thermal plume generated the concept that efficiency is the ratio of moisture cap by the cooktop but not so far forward that it will interfere tured by the hood to moisture produced by the source. with vision or food preparation. Using Figure 7 this can be stated as The capture function applies to residential hoods, but commercial hoods utilize a completely different mecha H = NE (1) nism to control pollutants-they use velocity to accom N, plish capture. The residential hood is a gravity capture device. (We sometimes call it a "Newtonian" hood.) or, for convenience in measuring and calculating, It is apparent that many factors govern the ability of the hood to capture cooking effl~ent, but to quantify the combined capture capability of a hood, a test standard was established. There is, at this time, an effort under way to F--- v 1--- - F have this e11tabli11hed &11 an indu11try te11t standard. Hood capture testing is accomplished in a sealed test room built of nonabsorbent materials. The room is 8 ft X 8 ft X 8 ft (Figure 6). Water vapor is used as the test medium and is produced by boiling water on a cooktop. Hood capture is determined by measuring the amount of vapor added to the room as opposed to that captured by the hood and removed from the room. Wet- and dry-bulb temperatures are measured at locations throughout the test Figure 7 N,,-N1t. where H=--- (2) N,. cs = moisture concentration at steady state (lb water/lb air). where Rearranging and combining Equations 2 and 6, hood capture efficiency (per unit), total production rate of moisture from source (lb NR N,.(1-H) c-c =-=---- (7) water/min), • ° F F rate of moisture captured by hood (lb Rearranging shows water/min), F rate of moisture escaping to room (lb H = 1 - - (c, - ca). (8) water/min). N,. Also at steady state, as illustrated by Figure 8, The general transient expression of the mass balance of moisture associated with the test room (referring back c,F = caF + N,.. (9) to Figure 7) is given by Rearranging shows F 1 v~~ = N,.(1-H)-Fc (3) - =-- (10) N,. c, - ca where Substituting into and combining with Equation 8, 3 1 . V room volume (ft ), H = 1---(c -c ). (11) c - c • 0 c moisture concentration (lb water/lb air), • 0 t time (min), And, finally, F = flow rate in and out of room (lb air/min). (12) The solution to this equation is Fca+NR] Fca+NR (4) c = e -~[ c.- +--- Thus, efficiency is given in terms of moisture con ' I F F centration at the various stations. The value of the concentration can be found by using the measured wet where bulb and dry-bulb temperatures. The humidity ratio, W, in pounds of water per pound moisture concentration at time t (lb water/lb air), of air, is given in ASHRAE Fundamentals (ASHRAE initial moisture concentration in room (lb 1985), page 6.13, as water/lb air), moisture concentration outside room (lb water/lb w = (1093 - 0.556 tw) w· - 0.240 (td - tw) = c (13) air), 1093 + 0.444 td - tw moisture concentration leaving room (lb water/lb air), where e natural log base (2.71828), T time constant of space (min/air change), defined dry-bulb temperature (°F), as wet-bulb temperature (°F), saturation humidity ratio at tw from Table 1, T = Vp (5) page 6.2. F where p air density (lb/ft3). At steady-state conditions with nonsaturated air, t = oo, Np e-t!T = O, and Equation 4 becomes (6) c, = c. = Figure 8 . 9 Using measured td and tw for air entering, leaving, and in , the room, it is possible to find c0 cs, and ce using Equation 13. These values of care then used in Equation . 8 12 to find hood capture efficiency. Using this test setup, we were able to test hundreds of variations in the parameters mentioned to arrive at . 7 optimum and economical hood shape designs. Hood capture efficiencies range between 50 % and 90 %, depen BLOWER WHEEL ding on the shape and size of the hood. w . 6 a:: :::J- (/) a:: How Hood Airflow Performance Is Measured (f)W wl- . 5 Cl: <.( The second factor in hood design is the airflow rate. Cl...3: (.) Over the years we have found that flow rates from 50 cfm f=z . 4 (cubic feet per minute) to 350 cfm can accommodate most Downdraft Ventilation The HVI has established a method for rating hoods and fans so they may be compared. Many years ago it Recent trends in cooking appliances have led to the was agreed that ventilating products would be given a development of the downdraft system. Some cooktops single-number rating of airflow (cfm) at a static pressure now have an air inlet grille leading to an air-moving of 0.1 inch of water. Through-the-wall fans would be device that exhausts air over and off the cooktop, sending rated at 0.03 inch of water. A single number is easily it down and out. These devices do not work on the understood in the field, especially when no engineer is thermal plume or Newtonian capture principle; rather, involved in the design and specification of a dwelling. they depend on the velocity capture principle where the It was decided by the HVI that the products would be contaminants are carried along by air moving fast enough tested in an engineering laboratory. This testing would to overcome convection. The disadvantage of this system follow the procedure outlined in ASHRAE Standard 51 is that much higher airflows are required to achieve this (AMCA 210). velocity, which means larger, more expensive blowers. It was also decided that hoods would be rated for Also, the fast-moving air cools the food being cooked and sound output with the sound reported in sones. Sones also may cool the gas or electric heating elements, were chosen over decibel ratings for their simplicity and slowing the cooking process. linearity. A rating of 4 sanes is perceived as twice as loud Downdraft units answer a need in island or peninsula as 2 sanes. The setup for the sound ratings was developed cooking installations where an updraft hood would be by the engineering committee of the HVI. Testing is done difficult to install and the downdraft can vent through the in a 5,755 ft3 reverberation chamber constructed with floor and out the side wall. There are downdraft units hard (reverberant), nonparallel surfaces. An anechoic today that are not iittegral with the cooktop but are muffler is used on the discharge of the chamber. Testing mounted separately behind or beside the cooktop. These compares a reference sound source, background level, and suffer from the same problem of having a high-velocity the tested devices over a frequency range including 24 air system that retards the cooking process. There are octave bands with center frequencies between 50 and models that lessen this problem by having the air inlet 10,000 Hz. This information is recorded and combined to move to a 6- to 10-inch height above and behind the give a measure of the sound experienced by a person 5 cooktop. Combining this feature with a speed control to feet from the test fan. The final result of this testing is a adjust to the required minimum airflow can result in fan sound rating in sanes. The exact mathematics is acceptable performance. Figure 11 shows such a unit. available in the HVI sound test procedure (HVI 1989). Figure 11 Additional Factors be adjusted to produce j~st enough airflow to remove the contaminants. That minimizes air noise. If a homeowner The results of the airflow testing and sound tests are forgets the hood is on, you have a successful hood published in the HVI Certified Products Directory, installation. published annually. The directory is a good means for making comparisons between different hoods and can aid in hood selection. Energy Consumption through Kitchen Ventilation In real life, the 0.1-inch static pressure does not always represent typical installations. Long duct runs, Energy consumption for intermittent kitchen ven elbows and transitions, terminal fittings, and flexible duct tilation consists of two components. The first is the cost can all increase the resistance to flow and should be of heating (or cooling) the makeup air required as a result considered when selecting a range hood. The sound rating of the hood's exhaust. The second is the direct cost of is only a guide to use for comparing hoods. The actual electricity to run the fan in the hood. mounting and surroundings will have a significant influ Since infiltration is always present, it is difficult to ence on the actual sound heard in an installation. The complaint heard most frequently about residential determine exactly how much to ascribe to range hood range hoods is related to the noise level of the hood. makeup air requirements. It has been reported that venting There are a number of possible reasons for this, and poor a clothes dryer did not significantly affect the infiltration design certainly can be one of the reasons. A good design rate (Olsen 1986). Nevertheless, a worst-case calculation can he made if one assumes that all of the makeup air is should have vibration isolation properly applied. It also "new" infiltration. For a complete heating season, the should minimize large unsupported sheet metal panels. It should avoid placing moving parts very close to stationary cost of heating makeup air using gas heat in any location can be calculated using the following equation: parts (blade note). It should pay particular attention to the electrical motors used in the hood; a poorly designed and 5 R = Q tc Y$ 60xlo- (14) used motor can be the worst offender in noise generation. p P ,. E An overexcited motor can result in excessive 60-Hz hum. Clearance problems and eccentricity can produce "beat" where frequencies. R total annual cost for the heatilij: season ($/year), The actual installation also may contribute to noise Q flow rate of exhaust (ft3 /min), problems. Loose mountings can cause excess vibration, p density of air (lb/fi3), which gtm.eraltls ex.c~s noise. Muunling Lu puurly con I ""' average llaily iunning lime of exhausl (h/day), structed and poorly installed cabinets also can contribute cp specific heat of air (Btu/°F/lb), to noise. Periodic cleaning helps to keep rotating parts in Y = annual total heating degree-days for locality (°F balance and therefore quiet. Blocked discharge ducts can · days/year), cause internal mixing, drumming, and noise. In the ideal $t cost per therm of energy ($/100,000 Btu), condition, the hood should be controlled so the speed can E heating system efficiency (unit/unit). ~ 0 The cost is so low that it often comes as a surprise. between houses heated by circulating Vs. nw.uu:ti If, for a very conservative example, it is assumed that heating systems. • ASHRAE Standard 62 will recognize that low-level Q = 100 ft3/min, continuous ventilation is not the equivalent of inter p = 0.075 lb/ft3, mittent ventilation, but that it can substitute for it if cp = 0.241 Btu/°F/lb, the system is carefully engineered and installed. t = running time of 1 h/day, • Continuous ventilation of the whole house will cease Y = 6,000 degree-days, to be the novelty it is today and will frequently be $, = $0.65 per therm (100,000 Btu) found in new construction. It will be accompanied by E = 0.65 efficiency, range hoods and bath fans for mitigation of high concentrations of intermittent sources. then the total annual cost of reheat, for the heating season is $6.501 To that can be added the cost of power for running the fan, F, SUMMARY F = Wtd$1:10·3 (15) Kitchen contaminants are both gases and particles of where a size similar to those found in cigarette smoke. The function and performance of conventionally F= total heating season cost for electricity to run the configured (updraft) range hoods has been studied and fan($), measured. They are very effective at controlling the w = power consumption of the fan (W), release of the contaminants into the rest of the living t = average daily running time of exhaust (h/day), space. d = annual heating days per year (days/year), The two functions (capture and flow) upon which a St = cost of electricity ($/kWh), hood depends for its performance are easily measured and identified. which, for the conservative example, comes to $1.50, An industry rating system and a knowledge of hoods plus the reheat cost of $6.50 from above, for a total are helpful in selecting and applying hoods for effective heating season cost of approximately $8.00. control of cooking contaminants at the source. It is best to A "real world" calculation is readily done, assuming select a hood that has a large, unobstructed capture sump. a bath fan for an hour per day, using values for Mil It is also important to select a hood that has a published waukee, Wisconsin, in 1991: (certified) air delivery higher than the minimum so it can be turned down to a lower flow rate for quieter perfor Q = 70 ft3/min, mance. That will encourage the homeowner to use the t = 1 h/day, hood and enhance indoor air quality. Y = 7 ,206 degree-days, S, = $0.3660 per therm (100,000 Btu), E = 0.75 efficiency, W = 70 watts, REFERENCES d = 140 days/year, $k = $0.0644 per kWh. ASHRAE. 1985. J985ASHRAE handbook-fundamentals. Atlanta: American Society of Heating, Refrigerating, Calculating results in a total heating season cost of $3. 30! and Air-Conditioning Engineers, Inc. Annis, S.C., and P.J. Annis. 1964. Kitchen range hood evaluations. Final report to FHA Contract HA-fn871, THE FUTURE OF KITCHEN VENTILATION Kansas State University. Cain, W.S., et al. 1979. Ventilation and odor control: Briefly, future trends in kitchen ventilation can be Prospects for energy efficiency. Report of University outlined as follows: of California, LBL subcontract no. 4622602, July. HVI. HVI certified home ventilating products directory. • Awareness will move consumers away from ductless Published annually. Arlington Heights, IL: Home hoods and toward ducted units. Ventilating Institute. • Downdraft ventilation will continue to be used, driven HVI. 1989. HVI procedure for loudness rating of residen by kitchen design style, but performance can suffer tial fan products. Arlington Heights, IL: Home Ven because it is anti-Newtonian. tilating Institute. • Automatic control of hoods is technically feasible and Olsen, W.W. 1986. Kitchen ventilation, purpose, selec will grow. tion and installation. Minnesota Extension Service, • Ventilation standards will begin to differentiate University of Minne8ota, HE-F0-2869-1986. t; Sarnosky, J.R. 1987. Air quality and pollution in the kitchen. Proceedings of the 38th Annual International Appliance Technical Conference. Traynor, G.W., D.W. Anthon, and C.D. Hollowell. 1981. Technique for determining pollution emissions from a gas fired range. Lawrence Berkeley Labora tory, University of California, LBL-9522. Wolhrink, D.W., P.H. Shair, L.H. Bowen, C.H. Neeley, and K.E. Sampsel. 1979. Influence of mechanical ventilation on moisture content of bathroom air. ASHRAE Journal, July.